The present invention relates to a loudspeaker. In particular, the invention relates to a loudspeaker of the upper bass/low mid type which may be used with loudspeakers covering other parts of the audible sound frequency spectrum in high quality public address (PA) systems.
The range or spectrum of audible sound frequencies is generally taken to extend from about 15 Hz to about 20 KHz. It is well known to divide this frequency range into several notional contiguous ranges with each such range being catered for by a loudspeaker whose design is largely dictated by the sub-range which it is required to handle. A typical example of such sub-ranges is as follows:
It has been found that the sub-ranges into which large PA systems are divided do not represent the best division of acoustic energy. Even in the best xe2x80x9cfour wayxe2x80x9d systems (i.e. systems having four sub-ranges), there is usually a xe2x80x9cmuddyxe2x80x9d and ill-defined frequency area straddling the used 150-200 Hz cross-over point between the bass and low mid sub-ranges. This unsatisfactory area extends from about 120 Hz to about 350 Hz.
According to a first aspect of the invention, there is provided an upper bass/low mid loudspeaker comprising: an electro-acoustic driver having a conical diaphragm and a housing and a central member defining a channel for the propagation of sound from the front of the diaphragm, the central member having a first portion extending into the volume defined by the diaphragm and defining with the diaphragm a first region of the channel of ring-shaped cross-section whose transverse cross-sectional area increases in the direction of sound propagation within the channel, the central member having a second portion disposed within a first portion of the housing to define a second region of the channel of ring-shaped cross-section whose transverse cross-sectional area decreases in the direction of sound propagation within the channel, the housing having a second portion defining a throat extending from the second region and a third portion defining a horn extending from the throat.
The first portion of the central member may have a transverse cross-sectional area which increases in the direction of sound propagation within the channel and the second portion of the central member may have a transverse cross-sectional area which decreases in the direction of sound propagation within the channel.
The throat may have a transverse cross-sectional area which increases at a first rate in the direction of sound propagation of sound within the channel. The horn may have a transverse cross-sectional area which increases at a second rate greater than the first rate in the direction of sound propagation within the channel.
The central member may have a third portion extending within the second portion of the housing and defining therebetween the throat which is of ring-shaped transverse cross-section. The central member may have a fourth portion extending into the horn. The fourth portion of the central member may have a substantially hemispherical end.
The central member may have a substantially circular transverse cross-sectional shape throughout its extent in the direction of sound propagation within the channel.
The housing may have a substantially rectangular transverse cross-sectional shape throughout its extent in the direction of sound propagation within the channel.
The housing may have a substantially parallel pair of internal surfaces.
The channel may be folded, for example at or adjacent the transition between the second region and the throat.
The loudspeaker may comprise an enclosure at the rear of the driver forming therewith a substantially sealed chamber.
According to a second aspect of the invention, there is provided a PA system including a loudspeaker according to the first aspect of the invention.
The term xe2x80x9cring-shapedxe2x80x9d as used herein means annular or isomorphic thereto. Thus, the central member is disposed inside the housing but does not touch it so that, at each cross-section transverse to the direction of sound propagation within the channel, the housing is spaced from the central member all the way around the central member.
The term xe2x80x9ctransverse cross-sectionxe2x80x9d as used herein means a section in a plane which is substantially perpendicular to the local direction of sound propagation within the channel.
It is thus possible to provide an upper bass/low mid loudspeaker which is capable of covering up to about a decade, for example from about 75 Hz to about 750 Hz. Within the upper bass/lower middle range of frequencies, a smooth frequency response, fast transient response and high efficiency (large acoustic output per watt of electrical power) can be provided. Furthermore, a good dispersion pattern, for example in the horizontal plane, can be provided. Such a loudspeaker is suitable for use in PA system, for example for concerts where high quality high level sound is required.
The unsatisfactory sound quality of known systems having a cross-over point around 150-200 Hz as mentioned hereinbefore can thus be overcome by providing an upper bass/low mid speaker with a range such that the cross-over points are well outside the troublesome area of 120-350 Hz. This allows a high quality PA system with a greatly improved division of acoustic energy and hence sound quality to be provided.